INVERTEBRATES

(not a classification group in its own right)

- NO BACKBONE
- COLD BLOODED
- GENERALLY SMALL (lessening problems
of gaseous exchange and circulation)
- MAINLY AQUATIC, some on land and in air

Names of the main groups are shown below, in capitals.
PHYLA (singular PHYLUM) - shown in bold - are the major groups, and CLASSES are the next subdivision.

Use the descriptions below to try to identify the (JUMBLED) numbered example organisms in the diagrams below, and write their numbers against the group names at the prompt: > .

COELENTERATES > 4 Hydra > 9 Portuguese Man o'war > 11 sea anemone
(new term: CNIDARIA)
- RADIALLY SYMMETRICAL

- TENTACLES and STING CELLS

Jellyfish, Sea Anemones, Corals (marine),
Hydra (freshwater)

ECHINODERMS > 5 starfish > 8 sea urchin

- tough SPINY SKIN

- RADIALLY SYMMETRICAL, with
5 radiating strips of TUBE FEET

- MARINE

Starfish & Sea Urchins

FLATWORMS (Some free-living,some parasites).
> 1 tapeworm > 2 liver fluke > 3 planarian > 10 flatworm

- dorso-ventrally flattened body !

Flukes, tapeworms, freshwater flatworms

NEMATODES (Roundworms, Eelworms, Threadworms, etc.) > 6 > 7

- THREADLIKE BODY - ROUND in cross-section - many PARASITES and DEBRIS FEEDERS.

What is the advantage to a simple organism of being A) radially symmetrical, and B) flattened?

>A) can react to stimuli/ take food from any direction

>B) no part of the body is far from the outside, so oxygen and food can diffuse easily

ANNELIDS > 12 earthworm > 15 leech > 22 ragworm

- ELONGATED BODY, divided into similar SEGMENTS, with bristles

- earthworms, Tubifex, etc.
- ragworms, lugworms, tubeworms, etc.
- leeches

MOLLUSCS > 13 scallop > 14 ramshorn snail > 25 cuttlefish
(use numbers again below)

- SOFT BODY, usually protected by CHALKY SHELL (greatly reduced in some cases)

- MUSCULAR "FOOT"

- Some are filter feeders.

GASTROPODS - SINGLE SHELL, may be coiled (snails, slugs,limpets) > 14 ramshorn snail

BIVALVES - TWO SHELLS (cockles, mussels, oysters, etc.) > 13 scallop

CEPHALOPODS - TENTACLES, very advanced (cuttlefish, squid, octopus) > 25 cuttlefish

ARTHROPODS ("jointed limbs")

- EXTERNAL SKELETON : hard cuticle

- outnumber rest of animal kingdom!

ARACHNIDS - 8 LEGS (spiders, scorpions,mites & ticks) > 19 spider > 23 scorpion

CENTIPEDES & MILLIPEDES - MANY LEGS > 22 centipede > 18 millipede

CRUSTACEANS - CHALKY cuticle (crabs, lobsters, shrimps, Daphnia, barnacles, woodlice)
> 17 Daphnia ("water flea") > 20 lobster

INSECTS - 6 LEGS (butterflies, moths, dragonflies, locusts, crickets, termites, bugs, beetles, ants, wasps, flies, etc.)
> 16 ant > 21 beetle

What are the advantages and disadvantages of a chalky outer layer (either shell or exoskeleton)?

> advantages: protection, against predators, water currents etc

> disadvantages: heavy (when out of water), must be in neutral/alkaline environment